One Radiator Not Getting Hot

It can be hard to identify if there is an issue with a TRV because you are actually trying the address symptom rather than the cause, which could be many other things other than a faulty TRV. The most common issue for which TRVs can be the cause is that there is one radiator that is not getting hot, while all the others in the house are.

It is important to work systematically and rule out potential issues, starting with the easiest to address:

1.Bleed the radiator

2.Check that the TRV is fitted correctly: Most TRV’s are now universal and can be fitted on the flow or the return however older ones were not. Generally this leads to noisy bangs so you would probably know this, however it will take seconds to check that the arrows on the valve are pointing in the right direction (or both directions for a universal valve). Note that they might be on the wall side of the valve, so you may have to feel for them

3.Check that the TRV has not seized or got stuck: You will need to remove the top of the TRV which contains the thermostat and then check to see that the plunger that operates the valve can be depressed. (See below or the video for full details about how to do this). It might be necessary to oil the plunger with a little WD40 or similar lubricant. If it stays stuck a careful knock with a hammer might just free it. If this does not work, then the TRV is fault and the best thing to do it replace the valve

4.Check the thermostat: If the valve is freely moving, and the radiator is working when the thermostat cap has been taken off, but stops again when you replace it, the thermostat is likely to be the problem. They work with an expanding wax capsule which can sometime solidify and stops the TRV working. Change this and it should start to work again

5.Check the lock shield valve: By now you will be pretty sure that the issue is not with your TRV, so you need to check the valve at the other end of the radiator. This is the lock shield valve and should be left open all the time while the heating system is operating normally. Check that this is open by opening it a little further or by closing and opening it again

6.Airlock or blockage: It is likely that if both valves are function properly then the problem is either a blockage or an airlock. You could try to force the water through by closing of all the other radiators and then turning the heating on, using the room thermostat. This just might produce enough pressure to force through the blockage, if you are lucky

7.Drain the Radiator: At this point you will have to drain the radiator, which could resolve the issue, however once you have gone to the trouble of doing this it is probably worth removing and trying to flush the radiator out before refitting it or even replacing it with a new one (depending on the state of the old one).

If one of your radiators is not getting hot, then this process should help you get to the bottom of the issue, and certainly fin or rule out the TRV at the cause. However prevention is the best cure, and there is a little simple maintenance that can be done which will make sure that you